Temperature dependence of the photoconductivity of arsenic-doped hydrogenated amorphous germanium thin films

Abstract We report a study of the photoconductivity (IPC) of As-doped a-Ge:H thin films as a function of temperature (T) and photon-flux (F). The experimental data discussed in this paper refer to the behavior of IPC at a fixed photon energy (1.3 eV) and at a fixed photon-flux (F≈2.4×10 16 cm −2 s −1 ) in the 14–380 K temperature range, as well as to the dependence of the exponent γ(IPC∝Fγ) on T (55–380 K) and on As-doping level, in the 8×10 14 –3×10 16 cm −2 s −1 photon-flux range. The measurement of IPC as a function of T indicates the presence of three distinct regions: (I) For T K ,I PC is poorly activated with T (activation energy ∼ few meV), (II) for 150 K K ,I PC is thermally activated with activation energies ranging between 122 and 167 meV, and (III) for T>260 K , a thermal quenching (TQ) of IPC is measured in all the As-doped a-Ge:H samples, the intensity of the TQ being enhanced with As doping. The measurement of IPC as a function of the photon-flux, at varying T, indicates the presence of a minimum for the exponent (γmin) at a Tmin. Both γmin and Tmin have their extreme values in the undoped sample and vary as the Fermi energy shifts from mid-gap to the conduction band edge.